<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
       
        var   i=prompt("输入你要输入得数");
        if(i<60){
            alert("不及格");
        }else  if(i>=60&&i<70){
            alert("合格");

        }else if(i>=70&&i<=80){
            alert("良好");
        }else{
            alert("优秀");
        }
    
    
    </script>
    
</body>
</html>